Abstract
Ethylene-Vinyl alcohol copolymers (EVA) were acetalized with formaldehyde (F-EVA), acetaldehyde (A-EVA) and n-butylaldehyde (B-EVA) in a solid state. The effects of acetalization on the sorption, the permeation and the diffusion of water vapor for EVA films were investigated. The results obtained are as follows. (1) The sorption isotherms of water vapor for all the acetalized EVA films could be described by sigmoid curves. The amount of the water sorbed in a mono layer, which is estimated from the BET equation, increased in the order of A-EVA, F-EVA and B-EVA. (2) Folry-Huggins' interaction paramete χ1 for A-EVA was lowest among those for acetalized EVA studied here. (3) Permeability coefficienst (P) increased with increasing the degree of acetalization, which is due to an increase in diffusion coefficient (D). (4) In the range of low relative humidity, D increased with relative humidity, which is associated with the breaking of the hydrogen bonding in the polymer. However, D approached to a constant value as the relative humidity became higher. This is due to the clustering of water molecules. (5) At the relative humidity when D attained a constant value, the logarithm of D was linearly related to the degree of acetalization.
